1. Technical Field
The invention relates to a novel amino acid, neo-tryptophan, as well as polypeptides containing this novel amino acid.
2. Background Information
Tryptophan is an essential component in human nutrition since it is not synthesized by the body. In addition, tryptophan is a hydrophobic amino acid that is part of many polypeptides.
Polypeptides as well as many other types of compounds such as neurotransmitters and drugs can exert profound effects on the body. For example, neurotensin (NT) is a tridecapeptide that induces antinociception and hypothermia upon direct administration to brain. Systemic administration of NT does not induce these effects since NT is rapidly degraded by proteases and has poor blood brain barrier permeability. Currently, two NT receptors have been identified and cloned. The first NT receptor is designated NTR1, while the second is designated NTR2. Both NTR1 and NTR2 are G-protein coupled receptors that are expressed by various brain tissues.
Serotonin (5HT) is a neurotransmitter that is essential to brain function. Multiple serotonin receptors and transporters have been identified and cloned. Briefly, de novo synthesis of serotonin from tryptophan occurs in the cytoplasm of a cell. Once synthesized, vesicular monoamine transporters package the transmitter into vesicular compartments so that its release can be regulated. Once released into the synapse upon proper stimulation, the transmitter can bind specific serotonin receptors, can be degraded by specific enzymes, and/or can be transported back into a cell by specific plasma membrane serotonin transporters and then re-packaged into vesicles. Thus, both serotonin receptors and transporters specifically recognize serotonin.
Apomorphine is an example of a drug that also influences brain function. Specifically, apomorphine is a non-selective dopamine D.sub.2 /D.sub.3 receptor agonist. At low doses, apomorphine (e.g., 25-200 .mu.g/kg) activates pre-synaptic receptors, while at higher doses (e.g., 600 .mu.g/kg) it influences post-synaptic sites. Thus, the behavioral affects of apomorphine vary with dosage. In mice and rats, high doses of apomorphine cause a characteristic climbing behavior as well as oro-facial stereotypies such as sniffing and licking behaviors. Using these high doses of apomorphine, atypical neuroleptic compounds have been identified based on their ability to block potently the climbing behavior while causing little change to the sniffing and licking behaviors. Both typical and atypical neuroleptic compounds have been used to treat schizophrenia and other psychotic disorders. Atypical drugs are preferred because of their lower propensity to cause motor side effects (e.g., extrapyramidal side effects such as parkinsonism and tardive dyskinesia).